DC-DC converter

ABSTRACT

A DC-DC converter and corresponding method for transitioning between a discontinuous conduction mode, DCM, and a continuous conduction mode, CCM, wherein the DC-DC converter is configured to power a signal processing system within an integrated circuit, is provided. The method comprises receiving input data, wherein the input data is for inputting into the signal processing system; determining an amplitude of the input data; and transitioning between DCM and CCM based on the amplitude of the input data. A DC-DC converter and respective method for transitioning from CCM to DCM comprising determining an estimated current representative of an inductor current through an inductor of the DC-DC converter; and transitioning from CCM to DCM based on the estimated current, is provided. A DC-DC converter and respective method for transitioning from DCM to CCM comprising determining either an output voltage of the DC-DC converter or a duty cycle of the DC-DC converter; and transitioning from DCM to CCM based on the determined output voltage or duty cycle of the DC-DC converter, is provided.

This application is a divisional of U.S. patent application Ser. No.15/984,965, filed May 21, 2018, which claims benefit to U.S. ProvisionalApplication Ser. No. 62/509,529, filed May 22, 2017, each of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

Embodiments disclosed herein relate to methods and apparatus fortransitioning a DC-DC converter between a discontinuous conduction mode(DCM) and a continuous conduction mode (CCM).

BACKGROUND

Portable devices are becoming more common in every aspect of our lives.For example, many consumers listen to their music from portable audioplayers. These portable devices become easier and more enjoyable to usewhen they are provided in small packages, offering the same capabilitieswhile still having long lasting battery charge. To support these longerlasting devices, the operating voltage of many of the components insideis often reduced to reduce the power consumption. However, thisreduction in operating voltage may affect the sound output of theportable device as the volume level of an audio signal is proportionalto the output voltage. Boost converters may therefore be used toincrease the operating voltage for select components within a portabledevice that would benefit from higher operating voltages, for example,audio amplifiers which may require high voltages to provide highvolumes.

FIG. 1 illustrates a conventional audio amplifier comprising a boostconverter. The audio amplifier comprises a battery supply 102 which isconfigured to provide a voltage V_(p) to a boost converter 104. Theboost converter 104 increases the voltage V_(p) to a boost voltageV_(BST). In this example, a speaker amplifier 108 is configured toreceive the boost voltage V_(BST) and to output an analog audio signal,SIG, from a digital to analog converter (DAC). The speaker amplifierincreases the low power signal, SIG, with the power received from theboost converter to generate a signal to drive a speaker 110. The boostvoltage V_(BST) is higher than the supply voltage V_(p) which allows thespeaker amplifier 108 to provide louder audio signals through thespeaker 110 than would be possible using only the supply voltage V_(p).

However, generating the boost voltage V_(BST) may have some drawbackssuch as increased power consumption of the audio amplifier 100. In otherwords, as the speaker amplifier is receiving the boost voltage V_(BST)then, even in circumstances where the volume levels are low, the speakeramplifier is wasting power compared to an implementation where it onlyreceives V_(p). This wasted power may shorten the operating time of thedevice comprising the audio amplifier between charges, and may bedetrimental to the user experience of the device.

In portable devices, operational battery life for a given charge cyclemay be considered critical. Consumers may request that end manufacturersproduce longer times between battery charging cycles. This request thenmay encourage the end manufacturers to require original equipmentmanagers (OEMs) and hardware developers to reduce operational powerconsumption in their sub-systems wherever possible, in order to extendbattery life between charging cycles. Boosted amplifiers may often beone of the heavy power consumers in a portable device containing audioamplification. Managing the operational transitions betweendiscontinuous conduction mode (DCM) and continuous conduction mode (CCM)is one method of managing power losses. CCM operation may be moreefficient than DCM when delivering higher output power. However, if theload requirements on the boost are reduced, the average current throughthe boost converter may also be reduced. However, CCM operation may pushand pull current through the inductor even when no power is consumed bythe load. This operation may produce losses through the inductor, forexample, switching losses, and cross conduction losses which may beunnecessary to maintain the boosted supply voltage (V_(BST)) during lowloading conditions. Transitioning over to DCM operation may thereforeallow the system to significantly reduce these losses while operating ina low or idle power loading conditions. Conversely, if the load on theV_(BST) supply is larger, operating in DCM may be less efficient thanoperating in CCM mode, and therefore the boosted system may operate inCCM mode in order to increase battery operational life for a givenboosted amplifier load.

SUMMARY

According to some embodiments there is provided a method in a DC-DCconverter for transitioning between a discontinuous conduction mode,DCM, and a continuous conduction mode, CCM, wherein the DC-DC converteris configured to power a signal processing system within an integratedcircuit. The method comprises receiving input data, wherein the inputdata is for inputting into the signal processing system; determining anamplitude of the input data; and transitioning between the DCM and theCCM based on the amplitude of the input data.

According to some embodiments, there is provided a method in a DC-DCconverter for transitioning from a continuous conduction mode CCM to adiscontinuous conduction mode, DCM. The method comprises determining anestimated current representative of an inductor current through aninductor of the DC-DC converter; and transitioning from CCM to DCM basedon the estimated current.

According to some embodiments, there is provided a method in a DC-DCconverter for transitioning from a discontinuous conduction mode, DCM,to a continuous conduction mode, CCM. The method comprises determiningeither an output voltage of the DC-DC converter or a duty cycle of theDC-DC converter; and transitioning from DCM to CCM based on thedetermined output voltage or duty cycle of the DC-DC converter.

According to some embodiments, there is provided a DC-DC converterconfigured to transition between a discontinuous conduction mode, DCM,and a continuous conduction mode, CCM, wherein the DC-DC converter isconfigured to power a signal processing system within an integratedcircuit. The DC-DC converter comprises a controller comprising an inputconfigured to receive input data for input into the signal processingsystem; a determination block configured to determine an amplitude ofthe input data; and a transitioning block configured to cause the DC-DCconverter to transition between the DCM and the CCM based on theamplitude of the input data.

According to some embodiments, there is provided a DC-DC converterconfigured to transition from a continuous conduction mode, CCM, to adiscontinuous conduction mode, DCM. The DC-DC converter comprises aninductor; and a controller comprising a current estimation blockconfigured to determine an estimated current representative of aninductor current through the inductor; and a transitioning blockconfigured to cause the DC-DC converter to transition from CCM to DCMbased on the estimated current.

According to some embodiments, there is provided a DC-DC converterconfigured to transition from a discontinuous conduction mode, DCM, to acontinuous conduction mode, CCM. The DC-DC converter comprises acontroller comprising a determination block configured to determineeither an output voltage of the DC-DC converter or a duty cycle of theDC-DC converter; and a transitioning block configured to cause the DC-DCconverter to transition from DCM to CCM based on the determined outputvoltage or duty cycle of the DC-DC converter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the embodiments of the present disclosure,and to show how it may be put into effect, reference will now be made,by way of example only, to the accompanying drawings, in which:—

FIG. 1 is an example block diagram of a conventional audio amplifiercomprising a boost converter in accordance with the prior art;

FIG. 2 is an example block diagram of a DC-DC converter in accordancewith an embodiment of the present disclosure;

FIG. 3a is an example timing diagram illustrating the operation of aboost converter in a continuous conduction mode, CCM, in accordance withan embodiment of the present disclosure;

FIG. 3b is another example timing diagram illustrating the operation ofa boost converter in a continuous conduction mode, CCM, in accordancewith an embodiment of the present disclosure;

FIG. 4 is an example timing diagram illustrating the operation of aboost converter in discontinuous conduction mode, DCM, in accordancewith an embodiment of the present disclosure;

FIG. 5 is an example flow chart diagram illustrating a method in a DC-DCconverter for transitioning between a discontinuous conduction mode,DCM, and a continuous conduction mode, CCM, in accordance with thepresent disclosure;

FIG. 6 is an example timing diagram illustrating an operation of a DC-DCconverter configured to transition between DCM and CCM as described inFIG. 5;

FIG. 7 is an example flow chart diagram illustrating a method in a DC-DCconverter for transitioning from a continuous conduction mode CCM to adiscontinuous conduction mode, DCM, in accordance with the presentdisclosure;

FIG. 8 is an example timing diagram illustrating an operation of a DC-DCconverter configured to transition from CCM to DCM as described in FIG.7;

FIG. 9 is an example flow chart diagram illustrating a method in a DC-DCconverter for transitioning from a discontinuous conduction mode, DCM,to a continuous conduction mode, CCM, in accordance with the presentdisclosure;

FIG. 10 is an example timing diagram illustrating an operation of aDC-DC converter configured to transition from CCM to DCM as described inFIG. 9;

FIG. 11 is an example timing diagram illustrating an operation of aDC-DC converter configured to transition from CCM to DCM as described inFIG. 9;

FIG. 12 is an example block diagram illustrating a DC-DC converter inaccordance with embodiments of the present disclosure;

FIG. 13 is another example block diagram illustrating a DC-DC converterin accordance with embodiments of the present disclosure;

FIG. 14 is a further example block diagram illustrating a DC-DCconverter in accordance with embodiments of the present disclosure.

DESCRIPTION

The description below sets forth example embodiments according to thisdisclosure. Further example embodiments and implementations will beapparent to those having ordinary skill in the art. Further, thosehaving ordinary skill in the art will recognize that various equivalenttechniques may be applied in lieu of, or in conjunction with, theembodiments discussed below, and all such equivalents should be deemedas being encompassed by the present disclosure.

FIG. 2 illustrates an example DC-DC converter 200 in accordance withembodiments of the present disclosure. The DC-DC converter 200 comprisesa battery supply 202 which provides a supply voltage V_(P) to the DC-DCconverter 200. The DC-DC converter 200 comprises an inductor 204connected to the battery supply 202. The DC-DC converter 200 furthercomprises two switches 206 and 208 and a capacitor 210. The switches 206and 208 are in this example implemented as an n-channel field effecttransistor (NFET) 206 and a p-channel field effect transistor (PFET)208.

In this example implementation, the inductor 204 is coupled to the drainterminal of the PFET 208 and the drain terminal of the NFET 206. Thedrain terminal of the PFET 208 and the drain terminal of the NFET 206are also coupled together.

The capacitor 210 is coupled between the source terminal of the PFET 208and ground. The source terminal of the NFET 206 is coupled to ground.Both the gate terminal of the PFET 208 and the gate terminal of the NFET206 are coupled to a controller 222 which controls whether the PFET 208and NFET 206 are in conducting or non-conducting states. An amplifier orother signal processing circuitry may be connected to receive the boostvoltage from the source terminal of the PFET 208.

For example, during a first time period, the NFET 206 may be switched onto a conducting state which couples the inductor 204 to ground, whilethe PFET 208 is switched off to a non-conducting state. This switchingconfiguration causes the supply voltage V_(P) to fall across theinductor 204 and therefore causes current to flow through the inductor204. The current flowing through the inductor 204 thereby stores energyin the inductor 204.

During a second time period, the NFET 206 may be switched off into anon-conducting state while the PFET 208 may be switched on to aconducting state. This switch configuration causes the inductor 204 tocouple to ground through the capacitor 210. Thus, the energy stored inthe inductor 204 during the first time period is transferred to thecapacitor 210 during the second time period. As energy is stored in thecapacitor 210, the voltage across the capacitor increases and allows theboost voltage V_(BST) to increase beyond the supply voltage V_(P).

A controller 222 may control the duration of the first and second timeperiods in order to regulate the transfer of power from the inductor 204to the capacitor 210 and thus regulate the level of the boost voltageV_(BST).

It will be appreciated that such a DC-DC converter 200 may operate intwo distinct modes: continuous conduction mode, CCM, and discontinuousconduction mode, DCM.

FIG. 3a illustrates the operation of a boost converter in a continuousconduction mode, CCM. In this state, the DC-DC converter 200 operateswith two switching states S₁ and S₂ per switching cycle. The controller222 may control the duty cycle of the switching states within eachswitching period. As previously described, during state S₁, NFET 206 isin a conducting state and PFET 208 is in a non-conducting state. Duringthis period, the current is drawn across the inductor 204 storing energyin the inductor 204. In switching state S₂, as described previously, thePFET 208 is in a conducting state and the NFET 206 is in anon-conducting state. During this period, the energy stored in theinductor 204 is transferred to the capacitor 210 and the current throughthe inductor drops.

The controller may control the length of the duty cycle in order tomaintain the output voltage, i.e. the boost voltage V_(BST), within apredefined range. In other words, if V_(BST) goes above a maximumvoltage V_(max), the time spent in state S₁ may be reduced and ifV_(BST) drops below a minimum voltage V_(min), then the time spent instate S₁ may be increased.

The switching state may be switched from state S₂ to state S₁ at thebeginning of each clock cycle as illustrated by the pulses indicatingthe start of each cycle of the switching frequency in FIG. 3 a.

However, when the load current decreases, in other words a higherresistance is coupled to receive the boost voltage V_(BST), the inductorcurrent also decreases. In this case, if the boost converter is left tooperate in continuous conduction mode, then the inductor current maybecome negative in each switching period, as illustrated in FIG. 3b .This negative current may waste power by passing negative current acrossthe inductor.

The boost converter may therefore be operated in discontinuousconduction mode (DCM). In DCM, there may be, for example, threedifferent switching states. The first and second switching states S₁ andS₂ may be the same as illustrated for CCM in FIGS. 3a and 3b , but in athird switching state S₃ both the NFET 206 and the PFET 208 may be in anon-conducting state.

As the PFET 208 is switched off, this switch deactivation stops anycurrent flowing back through the inductor in a negative direction,thereby pinning or maintaining the inductor current at 0 A asillustrated in FIG. 4. This mode therefore avoids wasting power by notallowing negative current through the inductor.

It may therefore be desirable to provide a method of switching betweenthe CCM mode illustrated in FIG. 3a and the DCM mode illustrated in FIG.4 dependent on the load on the DC-DC converter 200.

The controller 222 of FIG. 2 may therefore also receive one or morevariables in order to control the operation of the DC-DC converter 200.In some examples, the controller 222 is configured to receive anindication of a signal SIG, which is for inputting into a signalprocessing system such as the speaker amplifier 108 in FIG. 1.

In some embodiments, the controller 222 is configured to receive anindication of the boost voltage V_(BST). For example, the DC-DCconverter 200 may comprise an analog to digital converter (ADC) 220configured to receive the boost voltage V_(BST) and output a digitalversion of the boost voltage to the controller 222.

In some embodiments, the controller 222 is configured to receive anindication of an estimated current representative of an inductor currentthrough the inductor 204. For example, the DC-DC converter may comprisea current mirror 218 configured to mirror the current through the NFET206, and thus the current through the inductor 204 during the switchingstate S₁. The mirrored current may then be input into an ADC 216 whichoutputs a digital version of the mirrored current to the controller 222.

The controller 222 may then control the length of the differentswitching periods based on the aforementioned variables.

FIG. 5 is an example flow chart that illustrates a method in a DC-DCconverter for transitioning between a discontinuous conduction mode,DCM, and a continuous conduction mode, CCM. In this embodiment, theDC-DC converter is configured to power a signal processing system, forexample an amplifier. The signal processing system and DC-DC convertermay be coupled together within an integrated circuit.

In this embodiment, the DC-DC converter utilizes the amplitude of inputdata which is input into the signal processing system to indicate theload of the DC-DC converter. In other words, if the amplitude of theinput data for the signal processing system is higher, then the load onthe DC-DC converter is higher.

In step 501, the DC-DC converter receives the input data, wherein theinput data is for inputting into the signal processing system. For theexample illustrated in FIG. 1, the input data may comprise the signal,SIG, and the signal processing system may comprise the speaker amplifier108.

In step 502, the DC-DC converter determines an amplitude of the inputdata.

In step 503, the DC-DC converter transitions between DCM and CCM basedon the amplitude of the input data. For example, responsive todetermining that the amplitude of the input data is below a firstthreshold value, the DC-DC converter may transition from operating inCCM to operating in DCM. Furthermore, responsive to determining that theamplitude of the input data is above a second threshold value, the DC-DCconverter may transition from operating in DCM to operating in CCM.

In some embodiments, the first threshold value and the second thresholdvalue are the same. In some embodiments, the first threshold value andsecond threshold value are different in order to avoid ping-pongingbetween the different modes of operation. In other words, if only onethreshold is used, the DC-DC converter may transition rapidly betweenoperating states when the amplitude of the input data hovers around thethreshold value.

In some embodiments, in order to prevent the ping-ponging betweendifferent modes of operation, a time-based hold may be applied toexiting CCM operation before entering DCM operation. This time hold issomewhat of a time-based hysteresis. However, exiting DCM operation mayoccur immediately following a threshold violation so that CCM mayproperly regulate the boost voltage V_(BST). Under heavy or rapidlyincreasing loading conditions, DCM may not be able to properly regulatethe boost voltage V_(BST).

FIG. 6 is an example timing diagram that illustrates an operation of aDC-DC converter configured to transition between DCM and CCM asdescribed in FIG. 5.

In this embodiment, the value of the amplitude of the input data iscompared to a threshold value A_(T) to determine whether to operate inDCM or CCM. In particular, if the amplitude of the input data is abovethreshold value A_(T), the DC-DC converter operates in CCM, and if theamplitude of the input data is below threshold value A_(T), the DC-DCconverter operates in DCM. In this example, only one threshold value isused, however, as described above in some embodiments, two thresholdvalues may be used.

In this example, the DC-DC converter transitions from CCM to DCMresponsive to the amplitude of the input data remaining below the firstthreshold value for a predetermined time. By waiting a predeterminedtime before transitioning between the modes of operation, the DC-DCconverter avoids ping-ponging between the two modes of operation.

For example, the DC-DC converter may comprise a filter counterconfigured to count clock cycles from when the amplitude first passesbelow the threshold A_(T), at time t1, until the amplitude passes backabove the threshold A_(T), at time t2. In this example, at the time t2,the filter counter has not yet counted to a predetermined number X ofclock cycles. The DC-DC converter may therefore not transition into DCM.However, at time t3, the amplitude passes below the threshold A_(T)again, and this time remains below the threshold long enough for thefilter counter to count X clock cycles. Therefore, at time t4, when thefilter counter counts X clock cycles, the DC-DC converter may transitioninto DCM.

Equivalently, the DC-DC converter may transition from DCM to CCMresponsive to the amplitude of the input data remaining above thethreshold value for a predetermined time.

As described previously with respect to FIGS. 3a and 4, the controller222 may alter the operating state from CCM to DCM by including an extraswitching state S₃ in which both switches 206 and 208 are in anon-conducting state.

FIG. 7 is an example flow chart that illustrates a method in a DC-DCconverter for transitioning from a continuous conduction mode CCM to adiscontinuous conduction mode, DCM. In this embodiment, the DC-DCconverter may power any signal processing system, for example anamplifier.

In step 701, the DC-DC converter determines an estimated currentrepresentative of an inductor current through an inductor of the DC-DCconverter. Such an example DC-DC converter is illustrated in U.S. Pat.No. 9,912,238 hereby incorporated by reference.

For example, the DC-DC converter may determine the estimated current bymeasuring the current through the inductor, for example using a currentmirror 218. The measured current may then be converted into digitalsamples.

For example, the current through the N-FET 206 may be measured. In otherwords, the current through the inductor may be measured during theswitching state S₁ of the switching cycle as the current is ramped up.The current may be measured using, for example a multi-bit ADC or twocomparators.

Based on the measurement of the current during the state S₁ period, themethod may then comprise estimating an inductive value of the inductorbased on the measured current. The current during the second time periodfor state S₂ may then be estimated based on the estimated inductance,the boost voltage V_(BST), and the supply voltage value. In someexamples, the estimated current comprises a peak inductor current. Insome examples, the estimated current comprises an average inductorcurrent. The average inductor current may be proportional to the loadcurrent. In some examples, the estimated current comprises an averagepeak inductor current. By taking an average of the peak inductorcurrent, any transient peaks in the inductor current may be removed,resulting in a more accurate representation of the load current.

In step 702, the DC-DC converter transitions from CCM to DCM based onthe estimated current. For example, the DC-DC converter may compare theestimated current to a threshold value I_(T), and, responsive to theestimated current being below the threshold value I_(T), the DC-DCconverter may transition from CCM to DCM.

FIG. 8 is an example timing diagram that illustrates an operation of aDC-DC converter configured to transition from CCM to DCM as described inFIG. 7.

In this embodiment, the estimated current I_(EST) representative of thecurrent through the inductor is compared to a threshold value I_(T) todetermine whether to transition from CCM to DCM. In particular, whenoperating in CCM, the estimated current passes below the thresholdI_(T), the DC-DC converter may transition to operating in DCM.

In this example, a filter counter starts to count clock cycles from whenthe estimated current first passes below the threshold I_(T) at time t1.At time t2, the estimated current passes back above the threshold valueI_(T). However, at this time, the filter counter has not yet counted apredetermined number X of clock cycles. The DC-DC converter does nottherefore transition into DCM. However, at time t3, the estimatedcurrent passes below the threshold I_(T) again, and this time remainsbelow the threshold long enough for the filter counter to count X clockcycles. Therefore, at time t4, when the filter counter counts X clockcycles, the DC-DC converter transitions into DCM.

The DC-DC converter therefore transitions from CCM to DCM responsive tothe estimated current remaining below the threshold value I_(T) for apredetermined time.

It will be appreciated, that due to the inductor current beingmaintained or pinned to zero when operating in DCM, the inductor currentmay not be used, in some circumstances, to transition from DCM to CCM.

In some examples, the DC-DC converter may transition from DCM to CCM asdescribed with reference to FIGS. 5 and 6, or with reference to FIGS. 9and 10.

FIG. 9 is an example flow chart that illustrates a method in a DC-DCconverter for transitioning from a discontinuous conduction mode, DCM,to a continuous conduction mode, CCM.

In step 901, the DC-DC converter determines either an output voltage ofthe DC-DC converter or a duty cycle of the DC-DC converter.

For example, as illustrated in FIG. 2, an ADC may be configured toreceive the boost voltage V_(BST) and to output a digital version of theboost voltage to the controller 222. Alternatively, the DC-DC convertermay determine the duty cycle as the on time of the NFET switch 206. Inparticular, the duty cycle in DCM may be determined as the time periodduring which the inductor current is increased. The duty cycle may insome embodiments be monitored by comparing the NFET on signal with areference on-signal generated by internal clocks using logic gates.

In step 902, the DC-DC converter transitions from DCM to CCM based onthe determined output voltage or duty cycle of the DC-DC converter. Forexample, the controller 222 may control the switching states of theDC-DC converter based on the output voltage or duty cycle.

For example, the controller 222 may compare the output voltage of theDC-DC converter to a first threshold value, and responsive to the outputvoltage being below the first threshold value may cause the DC-DCconverter to transition from DCM to CCM. In other words, as the outputvoltage of the DC-DC converter is low, this low value may indicate thatthe inductor 204 is not being charged enough to keep the boost voltagewithin a desired range. The controller may therefore switch the DC-DCconverter to CCM in order to allow the boost voltage to be increased.

In some embodiments, the controller 222 compares the duty cycle of theDC-DC converter to a second threshold value, and responsive to the dutycycle being above the second threshold value, the DC-DC convertertransitions from DCM to CCM. In other words, when the load increases,the time taken to reach a maximum current during state S₁ increases, andtherefore the duty cycle increases. Contrary to CCM, during DCM it isknown that the current through the inductor starts at zero at the startof the state S₁ period, and therefore the duty cycle may be used as anindication of the load during DCM.

FIG. 10 is an example timing diagram that illustrates an operation of aDC-DC converter configured to transition from CCM to DCM as described inFIG. 9.

As illustrated in FIG. 10, the DC-DC converter may transition from DCMto CCM responsive to the output voltage being below the first thresholdvalue for a predetermined time. This manner of transition avoidsping-ponging between the two modes of operation.

In the example illustrated in FIG. 10, the output voltage of the DC-DCconverter is compared to a threshold value VT to determine whether totransition from DCM to CCM. In particular, when operating in DCM, theoutput voltage passes below the threshold VT, the DC-DC converter maytransition to operating in CCM.

In this example, the DC-DC converter comprises a filter counterconfigured to count clock cycles from when the output voltage firstpasses below the threshold VT at time t1 to when the output voltagepasses back above the threshold VT at time t2. In this example, thefilter counter has not yet counted a predetermined number X of clockcycles at time t2. The DC-DC converter may therefore not transition intoCCM. However, at time t3, the output voltage passes below the thresholdVT again, and this time remains below the threshold long enough for thefilter counter to count X clock cycles. Therefore, at time t4, when thefilter counter has counted X clock cycles, the DC-DC converter maytransition into CCM.

Equivalently, as illustrated in FIG. 11 the DC-DC converter maytransition from DCM to CCM responsive to the duty cycle remaining abovethe second threshold value for a predetermined time. Again, this avoidsping-ponging between the two modes of operation.

In the example illustrated in FIG. 11, the duty cycle of the DC-DCconverter is compared to a threshold value D_(T) to determine whether totransition from DCM to CCM. In particular, when operating in DCM, theduty cycle passes above the threshold D_(T), the DC-DC converter maytransition to operating in CCM.

In this example, the DC-DC converter comprises a filter counterconfigured to count clock cycles from when the duty cycle first passesabove the threshold D_(T) at time t1 to when the duty cycle passes backbelow the threshold D_(T) at time t2. In this example, the filtercounter has not yet counted a predetermined number X of clock cycles attime t2. The DC-DC converter may therefore not transition into CCM.However, at time t3, the duty cycle passes above the threshold D_(T)again, and this time remains above the threshold long enough for thefilter counter to count X clock cycles. Therefore, at time t4, when thefilter counter has counted X clock cycles, the DC-DC converter maytransition into CCM.

FIG. 12 illustrates a DC-DC converter 1200 according to someembodiments. The DC-DC converter 1200 is configured to transitionbetween a discontinuous conduction mode, DCM, and a continuousconduction mode, CCM. In particular, the DC-DC converter 1200 isconfigured to power a signal processing system within an integratedcircuit. The DC-DC converter 1200 comprises a controller 1201. Thecontroller 1201 may be equivalent to the controller 222 illustrated inFIG. 2. The controller 1201 comprises an input 1202 configured toreceive input data for input into the signal processing system. TheDC-DC converter 1200 further comprises a determination block 1203configured to determine an amplitude of the input data. The DC-DCconverter further comprises a transitioning block 1204 configured tocause the DC-DC converter to transition between the DCM and the CCMbased on the amplitude of the input data.

For example, the transitioning block may comprise a level shifting anddriving block configured to alter the switching states of the DC-DCconverter.

The DC-DC 1200 converter may comprise an NFET, a PFET switch, aninductor and a capacitor connected as described with reference to FIG.2. However, it will be appreciated that other implementations of boostconverters may also be used.

FIG. 13 illustrates a DC-DC converter 1300 according to someembodiments.

The DC-DC converter 1300 comprises an inductor 1301 and a controller1302. The controller comprises a current estimation block 1303configured to determine an estimated current representative of aninductor current through the inductor 1301. In some embodiments, thecurrent estimation block may comprise a current mirror and an ADC. Thecontroller further comprises a transitioning block 1304 configured tocause the DC-DC converter to transition from CCM to DCM based on theestimated current. For example, the transitioning block may comprise alevel shifting and driving block configured to alter the switchingstates of the DC-DC converter.

The DC-DC 1300 converter may comprise an NFET, a PFET switch and acapacitor connected as described with reference to FIG. 2. However, itwill be appreciated that other implementations of boost converters mayalso be used.

FIG. 14 illustrates a DC-DC converter according to some embodiments.

The DC-DC converter 1400 may be configured to transition from adiscontinuous conduction mode, DCM, to a continuous conduction mode,CCM. The DC-DC converter comprises a controller 1401 comprising adetermination block 1402 configured to determine either an outputvoltage of the DC-DC converter or a duty cycle of the DC-DC converter.

For example, the determination block may comprise an ADC configured toreceive the output voltage of the DC-DC converter, V_(BST), and tooutput a digital version of the output voltage. The controller maycomprise a transitioning block 1403 configured to cause the DC-DCconverter to transition from DCM to CCM based on the determined outputvoltage of the DC-DC converter.

In some examples, the transitioning block 1403 may be configured tocontrol the switching states of the switches 1404 and 1405 in the DC-DCconverter. When operating the DCM, the duty cycle of the DC-DC convertermay be determined as the state S₁ period as described with respect toFIG. 4.

In some embodiments, the determination block may receive an indicationof the duty cycle from the transitioning block and may cause thetransitioning block to transition from DCM to CCM based on thedetermined duty cycle.

There is therefore provided methods and apparatus for transitioning aDC-DC converter between a continuous conduction mode when high loads arepresent, and a discontinuous conduction mode when low modes are present.The transition between the two modes at an appropriate time dependent onthe load allows the DC-DC converter to save power.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. The word “comprising” does not excludethe presence of elements or steps other than those listed in the claim,“a” or “an” does not exclude a plurality, and a single feature or otherunit may fulfill the functions of several units recited in the claims.Any reference numerals or labels in the claims shall not be construed soas to limit their scope. Terms such as amplify or gain include possibleapplying a scaling factor or less than unity to a signal.

The invention claimed is:
 1. A method in a DC-DC converter fortransitioning from a discontinuous conduction mode, DCM, to a continuousconduction mode, CCM, the method comprising: determining either anoutput voltage of the DC-DC converter or a duty cycle of the DC-DCconverter; and transitioning the DC-DC converter from the DCM to the CCMbased on the determined output voltage or duty cycle of the DC-DCconverter.
 2. The method of claim 1 further comprising: comparing theoutput voltage of the DC-DC converter to a first threshold value, andresponsive to the output voltage being below the first threshold valuethe transitioning from the DCM to the CCM.
 3. The method of claim 2further comprising transitioning the DC-DC converter from the DCM to theCCM responsive to the output voltage being below the first thresholdvalue for a predetermined time.
 4. The method of claim 1 furthercomprising: comparing the duty cycle of the DC-DC converter to a secondthreshold value, and responsive to the duty cycle being above the secondthreshold value, transitioning the DC-DC converter from the DCM to theCCM.
 5. The method of claim 4 further comprising transitioning the DC-DCconverter from the DCM to the CCM responsive to the duty cycle remainingbelow the second threshold value for a predetermined time.
 6. The methodof claim 1 further comprising: determining an estimated currentrepresentative of an inductor current through an inductor of the DC-DCconverter; and transitioning the DC-DC converter from the CCM to the DCMbased on the estimated current.
 7. A DC-DC converter configured totransition from a discontinuous conduction mode, DCM, to a continuousconduction mode, CCM, the DC-DC converter comprising a controllercomprising: a determination block configured to determine either anoutput voltage of the DC-DC converter or a duty cycle of the DC-DCconverter; and a transitioning block configured to cause the DC-DCconverter to transition from the DCM to the CCM based on the determinedoutput voltage or duty cycle of the DC-DC converter.
 8. A DC-DCconverter of claim 7 wherein the transitioning block is configured tocause the DC-DC converter to transition from the DCM to the CCMresponsive to the output voltage being below a first threshold value. 9.The DC-DC converter of claim 8 wherein the transitioning block isconfigured to cause the DC-DC converter to transition from the DCM tothe CCM responsive to the output voltage remaining below the firstthreshold value for a predetermined time.
 10. The DC-DC converter ofclaim 7 wherein the transitioning block is configured to cause the DC-DCconverter to transition from the DCM to the CCM responsive to the dutycycle being above a second threshold value.
 11. The DC-DC converter ofclaim 10 wherein the transitioning block is configured to cause theDC-DC converter to transition from the DCM to the CCM responsive to theduty cycle remaining above the second threshold value for apredetermined time.